Scientists Study How We Evolved To Stand On Our Own Two Fins

Researchers raised two groups of walking, air-breathing Polypterus senegalus — one on land and one on the water. They discovered that each group was able to adapt to be best suited to its environment.

A. Morin, E.M. Standen, T.Y. Du, H. LarssonMcGill University

Scientists examining an unusual African fish that can walk and breathe air think they've learned a thing or two about how our distant ancestors made the leap from the oceans to terra firma some 400 million years ago.

The modern fish they studied is called Polypterus senegalus, which has both gills and lungs, as well as a remarkable ability to use its pectoral fins for locomotion. The lobe-like fins are positioned so the fish can walk, albeit awkwardly. Polypterus "looks very similar to the ancient fish that eventually evolved into tetrapods. That's why scientists examined this species in order to learn a bit more about its unusual characteristics," Science World Report says.

The Toronto Star writes that the results of the study, carried out by researchers from McGill University in Montreal and published in Nature, "suggest much about the evolution of complex pieces of anatomy such as arms and legs."

"What we wanted to pin down was: If you change the environment of this fish, does it change its behavior or does its anatomy change?" said Emily Standen, now at the University of Ottawa.

The Star reports that Standen and her colleagues "took two groups of Polypterus, raising one in water and one on land. They found that by the end of the experiment, the land-raised group had indeed become more efficient walkers than their aquatic counterparts."

According to the newspaper:

"But more interestingly, the landlubbers' bodies had also changed. Bones in their fins had grown beefier. And just a subtle hint of what might be glancingly referred to as a neck had also emerged.

"Even more interestingly, the changes seen in the walking group looked a lot like the changes seen in the fossil record as fish slowly evolved for terrestrial life."

The African fish that had been raised on land "walked more effectively by placing their fins closer to their bodies, lifted their heads higher, and kept their fins from slipping as much as fish that were raised in water," according to a statement from the researchers.

"Anatomically, their pectoral skeleton changed to become more elongate with stronger attachments across their chest, possibly to increase support during walking, and a reduced contact with the skull to potentially allow greater head/neck motion," said Trina Du, a McGill University Ph.D. student and study collaborator.

"Because many of the anatomical changes mirror the fossil record, we can hypothesize that the behavioral changes we see also reflect what may have occurred when fossil fish first walked with their fins on land," said Hans Larsson, one of the researchers.